Arc detection on alternating current (AC) power lines are known in the art. Examples of prior art detectors include U.S. Pat. No. 4,694,402 to McEachern et al.; U.S. Pat. No. 5,229,651 to Baxter et al. and U.S. Pat. No. 5,452,223 to Zuercher et al. McEachern et al. teach the comparison of adjacent cycles to detect waveform disturbances. Baxter et al. teach the comparison of the current cycle to a reference cycle built up from many prior cycles and Zuercher et al. teach the use of cumulative difference signals at predetermined points over many cycles to detect arcs. However, the McEachern et al. and Baxter et al. comparison signals suffer from nuisance tripping caused by varying loads. This limitation is addressed in Zuercher et al. by further analysis of the signal to detect arcs. All three approaches require relatively costly, power-hungry, fast digital processing because a plurality of points per cycle need to be sampled.